Hydrostatic seal with asymmetric beams for anti-tipping

ABSTRACT

A hydrostatic advanced low leakage seal configured to be disposed between relatively rotatable components. The seal includes a base. The seal also includes a shoe extending circumferentially. The seal further includes a first beam operatively coupling the shoe to the base, the first beam having a first thickness. The seal yet further includes a second beam operatively coupling the shoe to the base, the second beam having at least a portion thereof with a second thickness that is less than the first thickness.

BACKGROUND

Exemplary embodiments pertain to the art of gas turbine engines and,more particularly, to a hydrostatic seal with asymmetric beams foranti-tipping.

Hydrostatic advanced low leakage seals, or hybrid seals, exhibit lessleakage compared to traditional knife edge seals while exhibiting alonger life than brush seals. Some hybrid seals may be used to sealbetween a stator and a rotor within a gas turbine engine. The hybridseal is mounted to one of the stator or the rotor to maintain a desiredgap dimension between the hybrid seal and the other of the stator androtor. The hybrid seal has the ability to ‘track’ the relative movementbetween the stator and the rotor throughout the engine operating profilewhen a pressure is applied across the seal. The hybrid seal trackingsurface is attached to a solid carrier ring via continuous thin beams.

In typical hybrid seal designs, two parallel beams support a shoe. Thebase of the seal has behavior that is characterized by a beam orientedtangentially to the rotor, such that deflection of the shoe remainsrelatively normal to the rotating surface. The shoe moves radiallytoward and away from the rotating surface at a desired radial gap thatis less than 0.010 inches. However, the nature of the bending of the twobeams in concert with each other is to create a small amount of shoerotation at the displaced end of the beams. This is simple beam bending,where the beam is defined by the two parallel beams joined together ateach end. A problem arises when added deflection capability is neededfor large relative rotor deflection due to operationally applied loads,especially gyroscopic precession due to yaw in a helicopter. Therelative shoe rotation can be greater than a desired radial gapdimension from one end of the shoe to the other, increasing the risk ofcontact between the shoe and the rotor.

BRIEF DESCRIPTION

Disclosed is a hydrostatic advanced low leakage seal configured to bedisposed between relatively rotatable components. The seal includes abase. The seal also includes a shoe extending circumferentially. Theseal further includes a first beam operatively coupling the shoe to thebase, the first beam having a first thickness. The seal yet furtherincludes a second beam operatively coupling the shoe to the base, thesecond beam having at least a portion thereof with a second thicknessthat is less than the first thickness.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the portion of thesecond beam that has the second thickness is an end region of the secondbeam.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the end region of thesecond beam is the end of the second beam that is closest to a maximumradial deflection location of the seal.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first beam and thesecond beam are radially spaced from each other, the second beam beinglocated radially closer to the shoe than the first beam is to the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first beam and thesecond beam are radially spaced from each other, the second beam beinglocated radially further to the shoe than the first beam is to the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the plurality of beamsare oriented substantially parallel to each other.

In addition to one or more of the features described above, or as analternative, further embodiments may include that at least one of thefirst beam and the second beam has a beam length that is substantiallyequal to or greater than a circumferential pitch of the shoe.

Also disclosed is a seal assembly disposed in a gas turbine engine. Theseal assembly includes a first component. The seal assembly alsoincludes a second component, the first component and the secondcomponent relatively rotatable components. The seal assembly furtherincludes a hydrostatic advanced low leakage seal disposed between thefirst component and the second component. The seal includes a baseoperatively coupled to one of the first component and the secondcomponent. The seal also includes a shoe extending circumferentially.The seal further includes a first beam operatively coupling the shoe tothe base, the first beam having a first thickness. The seal yet furtherincludes a second beam operatively coupling the shoe to the base, thesecond beam having at least a portion thereof with a second thicknessthat is less than the first thickness.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first component isa stator and the second component is a rotor.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the seal isoperatively coupled to the stator.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the seal isoperatively coupled to the rotor.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the portion of thesecond beam that has the second thickness is an end region of the secondbeam.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the end region of thesecond beam is the end of the second beam that is closest to a maximumradial deflection location of the seal.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first beam and thesecond beam are radially spaced from each other, the second beam beinglocated radially closer to the shoe than the first beam is to the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first beam and thesecond beam are radially spaced from each other, the second beam beinglocated radially further to the shoe than the first beam is to the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the plurality of beamsare oriented substantially parallel to each other.

In addition to one or more of the features described above, or as analternative, further embodiments may include that at least one of thefirst beam and the second beam has a beam length that is substantiallyequal to or greater than a circumferential pitch of the shoe.

Further disclosed is a gas turbine engine including a compressorsection, a combustor section, a turbine section, and a seal assemblydisposed in a gas turbine engine, the seal assembly comprisingrelatively rotatable components and a hydrostatic advanced low leakageseal disposed between the relatively rotatable components. The sealincludes a base operatively coupled to one of the first component andthe second component. The seal also includes a shoe extendingcircumferentially. The seal further includes a first beam operativelycoupling the shoe to the base, the first beam having a first thickness.The seal yet further includes a second beam operatively coupling theshoe to the base, the second beam oriented substantially parallel to thefirst beam and having at least a portion thereof with a second thicknessthat is less than the first thickness, at least one of the first beamand the second beam having a beam length that is substantially equal toor greater than a circumferential pitch of the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first beam and thesecond beam are radially spaced from each other, the second beam beinglocated radially closer to the shoe than the first beam is to the shoe.

In addition to one or more of the features described above, or as analternative, further embodiments may include that the first beam and thesecond beam are radially spaced from each other, the second beam beinglocated radially further to the shoe than the first beam is to the shoe.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings, like elements are numberedalike:

FIG. 1 is a side, partial cross-sectional view of a gas turbine engine;

FIG. 2 is a perspective view of a portion of a hybrid seal assembly;

FIG. 3 is a perspective view of a radial deflection limiting element;

FIG. 4 is a seal portion engaged with the radial deflection limitingelement;

FIG. 5 is a comparison of a plurality of seals having a different numberof shoes;

FIG. 6A illustrates a finite element analysis of a first beamconfiguration of the hybrid seal assembly;

FIG. 6B illustrates a finite element analysis of a second beamconfiguration of the hybrid seal assembly;

FIG. 6C illustrates a finite element analysis of a third beamconfiguration of the hybrid seal assembly; and

FIG. 7 is a view of the hybrid seal assembly illustrating shoe tipping.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. The fan section 22 drivesair along a bypass flow path B in a bypass duct, while the compressorsection 24 drives air along a core flow path C for compression andcommunication into the combustor section 26 then expansion through theturbine section 28. Although depicted as a two-spool turbofan gasturbine engine in the disclosed non-limiting embodiment, it should beunderstood that the concepts described herein are not limited to usewith two-spool turbofans as the teachings may be applied to other typesof turbine engines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through aspeed change mechanism, which in exemplary gas turbine engine 20 isillustrated as a geared architecture 48 to drive the fan 42 at a lowerspeed than the low speed spool 30. The high speed spool 32 includes anouter shaft 50 that interconnects a high pressure compressor 52 and highpressure turbine 54. A combustor 56 is arranged in exemplary gas turbine20 between the high pressure compressor 52 and the high pressure turbine54. An engine static structure 36 is arranged generally between the highpressure turbine 54 and the low pressure turbine 46. The engine staticstructure 36 further supports bearing systems 38 in the turbine section28. The inner shaft 40 and the outer shaft 50 are concentric and rotatevia bearing systems 38 about the engine central longitudinal axis Awhich is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion. It will be appreciated that each of the positions of the fansection 22, compressor section 24, combustor section 26, turbine section28, and fan drive gear system 48 may be varied. For example, gear system48 may be located aft of combustor section 26 or even aft of turbinesection 28, and fan section 22 may be positioned forward or aft of thelocation of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five (5:1). Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present disclosure isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet (10,688 meters). The flight condition of 0.8 Mach and35,000 feet (10,688 meters), with the engine at its best fuelconsumption—also known as “bucket cruise Thrust Specific FuelConsumption (‘TSFC’)”—is the industry standard parameter of lbm of fuelbeing burned divided by lbf of thrust the engine produces at thatminimum point. “Low fan pressure ratio” is the pressure ratio across thefan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The lowfan pressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.45. “Low corrected fan tip speed” is theactual fan tip speed in ft/sec divided by an industry standardtemperature correction of [(Tram ° R)/(518.7° R)]^(0.5). The “Lowcorrected fan tip speed” as disclosed herein according to onenon-limiting embodiment is less than about 1150 ft/second (350.5 m/sec).

FIG. 2 schematically illustrates a hydrostatic advanced low leakageseal, or hybrid seal, indicated generally at 100. Although the hybridseal 100 is mounted on a stator in some embodiments, it will beappreciated that the hybrid seal 100 could alternatively be mounted to arotor. The hybrid seal 100 is intended to create a seal of thecircumferential gap between two relatively rotating components, such asa fixed stator and a rotating rotor. The hybrid seal 100 includes a baseportion 107 and at least one, but often a plurality of circumferentiallyspaced shoes 108 which are located in a non-contact position along theexterior surface of the rotor. Each shoe 108 is formed with a sealingsurface 110. For purposes of the present disclosure, the term “axial” or“axially spaced” refers to a direction along the longitudinal axis ofthe stator and rotor, whereas “radial” refers to a directionperpendicular to the longitudinal axis.

Under some operating conditions, it is desirable to limit the extent ofradial movement of the shoes 108 with respect to the rotor to maintaintolerances, such as the spacing between the shoes 108 and the facingsurface of the rotor. The hybrid seal 100 includes at least onecircumferentially spaced spring element 114. Each spring element 114 isformed with at least one beam 116.

Particularly when the hybrid seal 100 is used in applications such asgas turbine engines, aerodynamic forces are developed which apply afluid pressure to the shoe 108, which is counter balanced with thespring 114, causing it to move radially with respect to the rotor. Theinitial assembly point has a defined radial gap between the shoe 108 andthe rotating surface, with no forces acting upon the shoe 108. Inoperation, the hybrid seal 100 is used to restrict flow between a highpressure region and a lower pressure region. The pressure drop acrossthe shoe 108 creates a radial force on the shoe which is counterbalanced by the spring 114. In operation, when the gap between the shoe108 and rotor increases, the pressure drop across the axial length ofthe seal shoe decreases. The reduction in pressure across the shoe 108reduces the radial force acting on the shoe 108 such that the forcebalance between the pressure force and the spring 114 force causes theshoe 108 to be pushed radially inwardly toward the rotor, thusdecreasing the gap. Conversely, in operation, when the gap closes belowa desired level, the pressure drop across the shoe 108 increases,causing an increase in radial pressure force, which overcomes the springforce, thus forcing the shoe 108 radially outwardly from the rotor. Thespring elements 114 deflect and move with the shoe 108 to create aprimary seal of the circumferential gap between the rotor and statorwithin predetermined design tolerances.

Energy from adjacent mechanical or aerodynamic excitation sources (e.g.rotor imbalance, flow through the seal, other sections of the engine,etc.) may be transmitted to the seal 100, potentially creating avibratory response in the seal 100. Such vibratory responses createvibratory stress leading to possible reduced life of the seal 100, andcan be large enough to cause unintended deflections of the shoes 108.The vibratory response of the shoes 108 at their natural frequencies,while interacting with mechanical excitation or aerodynamic flow throughthe system, can reinforce each other causing unwanted vibration levelsand possible deflection of the shoes 108 as the vibration is transmittedto all of the shoes 108. Because the resonant frequency response is afunction of the square root of the ratio of spring element 114 stiffnessto the mass, design considerations include increasing the first ordernatural frequency by reducing the mass of the shoes 108 and/orincreasing the stiffness of the beams 116.

Increasing the stiffness of the beams 116 can only be considered if theavailable pressure drop is still sufficient to deflect the shoe 108relative to the rotor. In practice, the beams have a very low springrate to maintain the force balance with the pressure drop across theshoe 108, and create the desired, small, controlled gap. The hybrid seal100 operation requires low stiffness beams, making it difficult toachieve large increases in the resonant frequency through stiffness. Forthis reason it is preferable to decrease shoe mass.

Decreasing the mass of the shoes 108, by increasing the number of shoes108 in the assembled hybrid seal 100 is beneficial. With conventionalhybrid seal designs, the length of the spring 114 would also decrease.However, the radial deflection limiters would impose a fixedcircumferential geometric constraint, due to manufacturing andstructural requirements and therefore the radial deflection limiterswould become a proportionally larger percentage of the circumferentialspace available for the spring 114 and the deflection limiters. Thus itcan be shown, increasing the shoe quantity to reduce the shoe 108 mass,would reduce the circumferential arc length available for shoe 108 andspring 114, and the deflection limiters would impose a proportionallygreater reduction in the spring 114 length, which results in a stifferspring 114. However, the pressure balance force is proportional to thearc length, and would require a reduction in spring stiffness tomaintain the ability to control the gap. For a given length of spring114, the practical means to reduce the stiffness is to reduce thethickness of the beams 116. In practice, the ability to design thinbeams is not only limited by manufacturing techniques, but can result inbeams which might be easily damaged during manufacture, assembly anduse. Therefore, it is desired to decouple the arc length of the shoe 108from the length of the spring 114.

Referring now to FIGS. 3 and 4, rather than relying on end stops andradial deflection limit features that extend completely, or nearlycompletely, between the shoe 108 and the base portion 107 of the seal100—as with prior hybrid seals—the embodiments disclosed herein includetab and slot features on adjacent shoes 108 that provide deflectionshared end stops. As shown in FIG. 4, a tab 120 extending from a firstshoe 108 a is in engagement with a slot feature 122 extending from asecond shoe 108 b that is adjacent shoe 108 a to limit radial deflectionof the seal. The radial deflection is limited by deflection limitingposts 124 extending axially from a rear support 126 of the structure towhich the seal 100 is mounted to, such as a stator. Each post 124 isdisposed within a respective aperture 128 that is defined by a structureextending radially from the shoe 108.

Each of the above-described deflection limiting features have a smallradial height impact, which allows for a reduction in mass of the shoes108 and providing an increased design space within the seal 100. Forexample, the location of the beams 116 becomes independent of the shoe108 since the beams 116 no longer must have a length that is less thanthe arc length of each shoe 108, as shown well in FIG. 2, without havingto increase the radial design space that would be required if the angleof the beams were required to be changed. Additionally, by maintainingthe same beam angle with the same length, the substantially parallelbeams 116 maintain a generally tangent orientation relative to arotating seal land and maintain the functionality of the seal 100, butallows the height and length of the beams 116 to become independent ofthe shoe 108 circumferential pitch.

FIG. 5 illustrates a comparison of four embodiments of the seal 100,with each having a different number of shoes 108 and therefore shoe arclengths. Each illustrated seal 100 includes beams 116 with a common beamlength. As shown, the arc length of each shoe 108 in each illustratedseal design does not impact or impair the ability to maintain a beamthat is substantially equal to or longer than the arc length of theshoes.

Referring again to FIG. 2, the term “beam length” used herein is definedby length L. The beam length L includes end segments 170, which join thebeams 116. The end segments 170 are part of the beams 116, either in anintegrally formed manner or via a joining process, and it is the overalllength of the beams 116 and the end segments 170 that constitute thebeam length. It is this beam length that is substantially equal to orlonger than the arc length, or circumferential pitch, of the shoes 108.“Substantially equal” to the arc length of the shoe 108 refers to 95% ormore of the shoe length.

The above-described embodiments illustrated in FIGS. 2-5 includesubstantially parallel beams 116 that may not be oriented tangentiallyto the rotor due to the extended beam length. In such embodiments, aswell as any other embodiment of a hybrid seal, reducing tipping of theshoe 108 is advantageous, as such tipping may result in contact betweenan end of the shoe 108 and the rotating sealing surface. “Tipping”, asused herein, refers to relative rotation of ends of the shoe 108 in alongitudinal (i.e., circumferential) direction of the shoe which occurswhen one end of the shoe is radially deflected to a greater extent thanthe other end of the shoe. As shown in FIG. 7, the average runningclearance 191 must increase if the magnitude of the tipping is such thatpossible shoe contact can occur at the ends of the shoe 108. The averageclearance may be one value, but the local clearance may be too small andcause local contact with the rotor 199, which is undesirable for longterm durability.

The embodiments described herein provide beam geometry that offsets thetendency for the shoe 108 to tip. As shown in FIGS. 6A-6C, threedifferent beam geometries are illustrated. In particular, eachillustrated embodiment includes a pair of substantially parallel beams,referred to as a first beam 116 a and 116 b. Each beam 116 a, 116 bextends from a first end 180 to a second end 182. These ends do notinclude the end segments 170 that join the beams. The three illustratedembodiments are images captured during a common computer simulation thatquantifies each configuration's tipping due to relative radialdeflection of ends of the shoe 108. As shown, minimum radial deflectionof the overall seal assembly occurs at location 190, while maximumradial deflection occurs proximate a first end 192 of the shoe 108 whenthe shoe(s) is moving radially outward. Comparing the maximum radialdeflection to radial deflection at a second end 194 of the shoe 108provides a difference that quantifies the amount of tipping of the shoe.

FIG. 6A includes beams 116 a, 116 b that have an equal thickness and aresubstantially symmetrical. Of the three illustrated embodiments (6A-6C),this beam geometry results in the greatest amount of tipping. As usedherein, beam thickness refers to a dimension of the beams that measuresa dimension generally normal to the beam length, while width refers tothe axial dimension of the beams. The beam length is defined above.

FIG. 6B includes beams 116 a, 116 b that are substantially parallel, butat least a portion of the first beam 116 a has a thickness that is lessthan the thickness of the second beam 116 b. In other words, the beamthat is further radially outward of the shoe 108 includes a portion thatis thinner than at least a portion of the other beam. In the illustratedembodiment, the region of the first beam 116 a proximate the first end180 is thinner than at least a portion of the second beam 116 b. Thisregion of the first beam 116 a may be thinner than any portion of thesecond beam 116 b or may be thinner than only a portion of the secondbeam 116 b, such as the first end 180 of the second beam 116 b. Thegeometry of the beams 116 a, 116 b of FIG. 6B results in about 11% lesstipping compared to the embodiment of FIG. 6A.

FIG. 6C includes beams 116 a, 116 b that are substantially parallel, butat least a portion of the second beam 116 b has a thickness that is lessthan the thickness of the first beam 116 a. In other words, the beamthat is further radially inward of the shoe 108 includes a portion thatis thinner than at least a portion of the other beam. In the illustratedembodiment, the region of the second beam 116 b proximate the first end180 is thinner than at least a portion of the first beam 116 a. Thisregion of the second beam 116 b may be thinner than any portion of thefirst beam 116 a or may be thinner than only a portion of the first beam116 a, such as the first end 180 of the first beam 116 a. The geometryof the beams 116 a, 116 b of FIG. 6C results in about 50% less tippingcompared to the embodiment of FIG. 6A.

It has been demonstrated that a beam having at least a portion thereofwith a smaller thickness—when compared to the other beam—reduces tippingof the shoe 108. By reducing tipping of the shoe 108, the risk ofcontact with the sealing surface is advantageously reduced, and aconsistently tight running clearance will be possible without excessiveinstances of incidental contact between the shoe and the rotatingsealing surface.

The term “about” is intended to include the degree of error associatedwith measurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A hydrostatic advanced low leakage sealconfigured to be disposed between relatively rotatable components, theseal comprising: a base; a shoe extending circumferentially; a firstbeam operatively coupling the shoe to the base, the first beam having afirst thickness; and a second beam operatively coupling the shoe to thebase, the second beam having at least a portion thereof with a secondthickness that is less than the first thickness, the first beam and thesecond beam extending past an end of the shoe, wherein the portion ofthe second beam that has the second thickness is an end region of thesecond beam.
 2. The seal of claim 1, wherein the end region of thesecond beam is an end of the second beam that is closest to a maximumradial deflection location of the seal.
 3. The seal of claim 1, whereinthe first beam and the second beam are radially spaced from each other,the second beam being located radially closer to the shoe than the firstbeam is to the shoe.
 4. The seal of claim 1, wherein the first beam andthe second beam are radially spaced from each other, the second beambeing located radially further to the shoe than the first beam is to theshoe.
 5. The seal of claim 1, wherein the first beam and the second beamare oriented substantially parallel to each other.
 6. The seal of claim1, wherein at least one of the first beam and the second beam has a beamlength that is substantially equal to or greater than a circumferentialpitch of the shoe.
 7. The seal of claim 1, wherein the first beam andthe second beam are each joined to each other via an end segment.
 8. Aseal assembly for use in a gas turbine engine, the seal assemblycomprising: a first component; a second component, the first componentand the second component being relatively rotatable components; and ahydrostatic advanced low leakage seal disposed between the firstcomponent and the second component, the seal comprising: a baseoperatively coupled to one of the first component and the secondcomponent; a shoe extending circumferentially; a first beam operativelycoupling the shoe to the base, the first beam having a first thickness;and a second beam operatively coupling the shoe to the base, the secondbeam having at least a portion thereof with a second thickness that isless than the first thickness, the first beam and the second beamextending past an end of the shoe, wherein the portion of the secondbeam that has the second thickness is an end region of the second beam.9. The seal assembly of claim 8, wherein the first component is a statorand the second component is a rotor.
 10. The seal assembly of claim 9,wherein the seal is operatively coupled to the stator.
 11. The sealassembly of claim 8, wherein the end region of the second beam is an endof the second beam that is closest to a maximum radial deflectionlocation of the seal.
 12. The seal assembly of claim 8, wherein thefirst beam and the second beam are radially spaced from each other, thesecond beam being located radially closer to the shoe than the firstbeam is to the shoe.
 13. The seal assembly of claim 8, wherein the firstbeam and the second beam are radially spaced from each other, the secondbeam being located radially further to the shoe than the first beam isto the shoe.
 14. The seal assembly of claim 8, wherein the first beamand the second beam are oriented substantially parallel to each other.15. The seal assembly of claim 8, wherein at least one of the first beamand the second beam has a beam length that is substantially equal to orgreater than a circumferential pitch of the shoe.
 16. The seal assemblyof claim 8, wherein the first beam and the second beam are each joinedto each other via an end segment.
 17. A gas turbine engine comprising: acompressor section; a combustor section; a turbine section; and a sealassembly disposed in the gas turbine engine, the seal assemblycomprising relatively rotatable components and a hydrostatic advancedlow leakage seal disposed between the relatively rotatable components,the seal comprising: a base operatively coupled to one of the relativelyrotatable components; a shoe extending circumferentially; a first beamoperatively coupling the shoe to the base, the first beam having a firstthickness; and a second beam operatively coupling the shoe to the base,the second beam oriented substantially parallel to the first beam andhaving at least a portion thereof with a second thickness that is lessthan the first thickness, at least one of the first beam and the secondbeam having a beam length that is greater than a circumferential pitchof the shoe.
 18. The gas turbine engine of claim 17, wherein the firstbeam and the second beam are radially spaced from each other, the secondbeam being located radially closer to the shoe than the first beam is tothe shoe.
 19. The gas turbine engine of claim 17, wherein the first beamand the second beam are radially spaced from each other, the second beambeing located radially further to the shoe than the first beam is to theshoe.
 20. The gas turbine engine of claim 17, wherein the first beam andthe second beam are each joined to each other via an end segment.